The primary objective of the research is a study of the regulation of expression of the genome during early embryological development. Particularly, this work concerns mechanisms of cell differentiation in the sea urchin embryo. The research will center on: 1) The arrangement of different types fo identifiable nucleotide sequence in and near transcription and replication regions on nuclear DNA, 2) regulation of transcription during cell differentiation, 3) processing of newly transcribed RNA sequences within the nucleus of the cell. The present and proposed work concerns sequence regions on bulk DNA and RNA as well as regions in fractionated DNA and RNA enriched for a specific sequence (e.g., sequences containing regions coding for histone genes). We are particularly interested in regions of the genome responsible for cell differentiation. The latter work also concerns the mechanism by which 5-bromodeoxyuridine turns off cell differentiation.